1. Field of the Invention
The present invention relates to a sintered polycrystalline diamond composite for use in rock drilling, machining of wear resistant materials, and other operations which require the high abrasion resistance or wear resistance of a diamond surface. Specifically, this invention relates to such bodies that include a polycrystalline diamond layer attached to a cemented carbide substrate via processing at ultrahigh pressures and temperatures.
2. Description of the Art
It is well known in the art to form a polycrystalline diamond cutting element by sintering diamond particles into a compact using a high pressure, high temperature (HP/HT) press and a suitable catalyst sintering aid. Apparatus and techniques to accomplish the necessary sintering of the diamond particles are disclosed in U.S. Pat. No. 2,941,248 to Hall and U.S. Pat. No. 3,141,746 to DeLai.
U.S. Pat. No. 3,745,623 Wentorf et al. teaches sintering of the diamond mass in conjunction with tungsten carbide to produce a composite compact (PDC) in which the diamond particles are bonded directly to each other and to a cemented carbide substrate.
Diamond compacts and PDC manufactured in accordance with the teachings of DeLai and Wentorf et al. have been limited to low-temperature applications since they show significant thermal damage at temperatures above approximately 750° C. The thermal degradation results in accelerated wear when such compacts are employed in high-temperature applications such as in rock drilling.
A solution to this problem has been proposed in U.S. Pat. No. 5,127,923 to Bunting whereby a diamond cutting element is produced by subjecting a mass of abrasive particles, e.g. diamond or cubic born nitride, to multiple pressure cycles at high temperatures. A solvent-catalyst sintering aid is employed in the initial pressure cycle to form a compact. Depending upon the degree of sintering, the solvent-catalyst can be removed by leaching or other suitable process. During a second pressure cycle, the compact can be bonded to a supporting substrate. In addition, a non-catalyst sintering aid, such as silicon, boron or metals rendered non-catalytic by the addition of silicon or boron which may form strong and chemically-resistant carbides, can be used in the second pressure cycle to enhance the sintering process and create a hard abrasive bonding matrix through out the particle mass.
A problem with this approach is that the polycrystalline diamond layer that is formed during the first high-pressure/high-temperature cycle must be precision ground prior to placing it on top of a substrate for the final high-pressure/high-temperature bonding step. This significantly increases the cost and results in a significantly lower yield than producing PDC in a single step operation. Another disadvantage is the bond between the polycrystalline diamond layer and the substrate is not nearly as strong as that for PDC which is made in a single high pressure cycle whereby individual diamond crystals are bonded to a substrate and to each other. The diamond layer on PDC made by this prior art method often spontaneously delaminates from the substrate before or during use on drill bits or other tools.
Another solution to this problem has been proposed in U.S. Pat. Nos. 6,878,447, 6,861,137, 6.861,098, 6,797,326, 6,739,214, 6,592,985, 6,589,640, 6,562,462 and 6,544,308 to Griffin. This solution provides a cutting element wherein a portion of the diamond table is substantially free of the catalyzing material, and the remaining diamond matrix contains the catalyzing material.
According to these patents, a portion of the diamond table of the PCD element is post-processed so that the interstices among the diamond crystals are substantially free of the catalyzing material. The portion of the diamond table that is substantially free of the catalyzing material is not subject to the thermal degradation encountered in other areas of the diamond body, resulting in improved resistance to thermal degradation. In cutting elements, the processed portion of the diamond body may be a portion of the facing table of the body, a portion of the peripheral surface of the body, or portions of all these surfaces.
A problem with this approach is that it is difficult to leach the catalyst sintering aid if the polycrystalline diamond working surface is highly consolidated with strong diamond to diamond bonding. Typically PDC for rock drilling is made from a blend of diamond with different particle sizes giving an average particle size of less than 25 microns. This results in a dense diamond table and it is very difficult to remove the catalyst. Even with diamond particle sizes as large as 40 microns it can become problematic to remove the catalyst if sintering conditions are such that extensive diamond to diamond bonding reduces the size of the interconnected pore network. To alleviate this problem addition of non-catalytic fillers or lower pressure sintering conditions are necessary in order to create a large enough area of interconnected pores so that acids or other materials can effectively penetrate the diamond network to remove the catalyst. This reduces the impact and abrasion resistance of the finished PDC.
Unlike PDC used in drag bits, cutting elements used in rotary bits to drill rock do not have a sharp cutting edge but must be able to withstand very high impact forces. PDC elements used for this type of bit have a diamond table with a convex dome shape. The PDC elements with a domed shape diamond table are not leached because the leached portion of the diamond results in lower impact resistance for this application. Thus it is generally thought that leaching the catalyst metal from a sintered diamond body does have a negative affect on the low temperature strength of the compact.
Guojlang proposes another solution in US patent application no. 2010/032006 A1. This approach to the problem is similar to that of Bunting whereby the PDC is manufactured in several high-pressure/high-temperature steps. A polycrystalline diamond layer is fabricated without the substrate in the first step is then attached to a substrate via high-pressure/high-temperature bonding in a second step. This patent explains the difficulty that arises in trying to re-infiltrate a previously sintered diamond layer. To enhance the capability of the catalyst metal to infiltrate the pre-sintered layer a number of channels or pathways are designed into the surface of the diamond layer that is to be attached to the substrate. This approach appears to have many of the same problems associated with the Bunting patent.
A significant improvement in the performance of PDC for rock drilling was accomplished by the introduction of a non-planar interface between the polycrystalline diamond layer and the substrate. This is well known in the art and many US and foreign patents have been issued describing numerous patterns for varying the shape of the surface that separates the diamond layer and the substrate. This improvement cannot be realized with PDC made by the methods taught in the Bunting or the Guojlang patents because it is extremely difficult to grind a non-planar diamond surface with close enough tolerances to correctly match the surface of a non-planar substrate. As a result, when one tries to attach a pre-sintered diamond layer to a substrate with a non-planar interface, cracks form in the diamond layer during the second high-pressure/high-temperature cycle. Catalyst metal flows into these cracks and prevents rebonding of the diamond and the resultant strength of the finished PDC cutting element is significantly reduced.
US patent application no. 2011/0083908 A1 to Shen describes a method wherein a first volume consisting of a presintered diamond table is bonded to a second volume of diamond that is either in the form of a presintered diamond table or loose individual single crystal diamonds. By bonding the two diamond bodies together at a lower pressure than that used to presinter the first body stress presumedly is reduced in the PDC. Using a presintered table in the second HPHT step results in the same cracking problems associated with the Bunting and Guojlang patents. If the diamond in the second HPHT step is loose abrasive beneath the first diamond table an uneven force distribution still exists especially with non-planer substrates and cracking of the presintered diamond table persists.
Both Griffin and Shen show presintered diamond pieces imbedded into loose individual single crystal diamonds. The presintered diamond pieces are made at higher pressures then incorporated into the final PDC in a lower pressure bonding cycle. This results in a cutting element with impact and abrasion characteristics determined by the properties of the second matrix. Additionally the second matrix makes it as difficult to remove the catalyst as it is for single matrix cutters.
A PDC cutting element is needed that has densely consolidated diamond with strong bonding, is thermally stable and can be readily manufactured with a non-planar interface between the diamond layer and the substrate if desired.